1. Field of the Invention
The present invention relates, in general, to nonvolatile semiconductor memory devices and, more particularly, to a circuit for indicating the termination of scan of bits to be programmed, which generates a scan termination signal indicating that a set number of bits to be programmed have been completely scanned.
2. Description of the Related Art
A nonvolatile semiconductor memory device, such as a flash memory device, has a function of electrically erasing stored data a field or string at a time and has low power consumption characteristics. Therefore, the nonvolatile semiconductor memory device has attracted attention as a recording medium for portable terminals, such as digital cameras and memory cards, in addition to permanent memory devices used for personal notebook computers, etc.
The state of data stored in the nonvolatile semiconductor memory device is determined by the threshold voltage of a transistor forming a memory cell. That is, different charges are stored in a floating gate of the memory cell, so that the threshold voltages of the transistor of the memory cell are changed to intended preset levels. Through this process, data stored in the memory cell is programmed to have states that can be identified in a read operation.
In the meantime, nonvolatile semiconductor memory devices are classified into NAND-type memory and NOR-type memory according to the form of the connection of memory cells to bit lines. In the case of a NAND-type nonvolatile semiconductor memory device, memory cells M11 to M14 form a string together with selection transistors ST1 and ST2, and are connected in series with each other between a bit line BL and a ground voltage VSS, as shown in FIG. 1. The programming of such a NAND-type nonvolatile semiconductor memory device is performed using Fowler-Nordheim (F-N) tunneling. In this case, since a Ground Selection Line (GSL) signal is in a logic L (low) state, the amount of current consumption is relatively low. Therefore, the NAND-type nonvolatile semiconductor memory device performs programming for all memory cells connected to a single word line (any of WL11 to WL14) through a single program operation.
In the meantime, in the case of a NOR-type nonvolatile semiconductor memory device, memory cells M21 to M26 are connected between a bit line BL1 or BL2 and a source line CSL, as shown in FIG. 2. Programming for such a NOR-type nonvolatile semiconductor memory device is performed using Channel Hot Electron (CHE) injection. In this case, a current path is formed between the bit line BL and the source line CSL, so that the amount of current consumption is relatively high. Accordingly, the NOR-type nonvolatile semiconductor memory device performs programming for memory cells, selected a column at a time to allow the number of memory cells to correspond to the number of set bits, through a single program operation. For this operation, in the NOR-type nonvolatile semiconductor memory device, a data scan operation of scanning a certain number of data bits to be programmed is performed. Further, the NOR-type nonvolatile semiconductor memory device includes a circuit for indicating the termination of scan of bits to be programmed therein to generate a scan termination signal. The scan termination signal indicates that a number of set data bits to be programmed have been completely scanned.
FIG. 3 is a view showing a conventional circuit 100 for indicating the termination of scan of bits to be programmed. A counter 110 counts the number of bits to be programmed, that is, the number of data bits scanned in a data scan operation and to be programmed. A group of counting bit signals CNT<n:0>, which indicates the number of bits to be programmed, is provided to a bit number attainment detection unit 120. Further, the bit number attainment detection unit 120 changes the logic level of a scan termination signal SCT when the number of bits to be programmed attains the number of set bits.
However, the conventional circuit 100 for indicating the termination of scan of bits to be programmed is problematic in that the number of set bits is fixed to a specific number set at the time of manufacturing a nonvolatile semiconductor memory device, and cannot be changed after the manufacture of the nonvolatile semiconductor memory device has been completed.